1. Field of the Invention
The present invention relates to drip irrigation, and in particular to a pressure controlled drip irrigation emitter and apparatus capable of maintaining a constant drip rate over a very wide range of pressure.
2. Description of the Prior Art
Several different varieties of drip irrigation emitters are known in the art. All drip irrigation emitters are associated in some way with a conduit line through which a pressurized fluid may flow. The fluid can be anything, but is typically water for growing plants, either by itself or with dissolved additives such as fertilizers or nutrients. Drip irrigation emitters may be attached to the end of a conduit line, attached along the outside of a conduit line, or inserted into the inside of a conduit line where there is a tiny hole that allows fluid to reach the outside. In every drip irrigation emitter, there is some means for allowing fluid inside the line to reach the outside at a very slow rate.
One of the most common and useful applications of drip irrigation is in hilly, uneven terrain. This is because normal flood or spray irrigation methods either do not work or are very wasteful of scarce water. It also is very common in the drip irrigation industry for drip irrigation conduit lines to be several hundred feet long or longer, attached to a single water source.
These common applications of drip irrigation pose several problems, the most serious relating to pressure. At low pressure, fluid simply flushes through some drip irrigation emitters. Emitters, such as those disclosed in U.S. Pat. Nos. 4,113,180 and 3,779,468 require the pressure inside the conduit line to reach a certain high level before the emitters on the line stop flushing and begin to "drip". The different gradients in hilly terrain generally cause a drip irrigation line to have different pressure levels at different places. A drip irrigation line that is several hundred feet long, even if on level ground, requires significant pressure to activate all of the drip irrigation emitters along its length. This problem is compounded in hilly, uneven terrain.
In order to respond to these problems, different types of drip irrigation emitters have been developed. These include devices such as those disclosed in U.S. Pat. Nos. 4,307,841 and 4,687,143. In each of these devices, a flat flexible membrane is provided on a platform. One side of the membrane is in contact with the fluid in the line, the other side is pressed against a flat surface with an opening to the outside. An elongated shallow groove is provided in the flat surface under the membrane leading from the opening to the edge of the surface. The fluid in the line presses the membrane against the surface and the opening so that at very low pressure only a tiny amount of fluid is allowed to escape through the opening. As pressure is increased, the opening is closed off and only by means of the groove is the fluid allowed to escape. However, when the pressure gets very high, the membrane tends to completely close off the opening and the groove preventing any fluid from escaping through the opening.
Very high pressure is usually required at the beginning of a conduit line in order to assure that at least some pressure reaches all of the line. The longer the line, the greater the initial pressure required. Further, in uneven terrain, lower locations on the line will naturally have higher pressure than higher locations.
Because of the way currently developed emitters are designed, they are not useful in lines where high pressure will be used (e.g. near the beginning of the line, or at a low spot) because at such pressures they tend to reduce the flow rate or close off completely. It is therefore desirable to have a drip irrigation emitter that not only operates at relatively low pressures, but which has a constant flow rate through a wide range of pressures, including very high pressures, without the flow rate dropping or the emitter shutting off completely.
Because of the high cost of materials, it is also desirable to be able to construct smaller drip irrigation emitter units that provide the same flow rates as larger units. Smaller units may be priced lower than larger units, and have the advantage that they can be used on small or large diameter lines. This becomes especially important where thousands of emitters are connected to miles of conduit line.
When pressure to a drip irrigation line is removed, a siphon or back flow can occur resulting in the drawing of dirt and debris into the drip irrigation emitters along the line. In order to avoid the clogging caused by this situation, it is also desirable to provide a way for such drip irrigation emitters to flush out such dirt and debris.